This invention relates to a strain relief structure for the power cord of a dynamoelectric machine (e.g., an electric motor).
Electric motors oftentimes provide a means for supporting or relieving strain from the electrical power cord supplying power to the motor. This may involve the use of a synthetic resin or other electrically insulative grommet inserted into an opening in the shell of the motor, with the grommet receiving and gripping the power lead. In that manner, in the event a tension or pulling load in any direction is applied to the power cord, the load is transmitted from the power cord to the structure of the electric motor without placing undue strain on the connections between the power cord and the lead wires of the windings of the motor. However, in certain motor applications where the motor moves relative to its power cord, there are requirements of testing agencies, such as Underwriters Laboratory (UL), that tension loads of a predetermined amount be capable of being transmitted from the power cord to the electric motor without damage to either the power cord or to the connections between the power cord and the motor lead wires.
More particularly, in an application for an electric motor utilized to power a radial arm wood saw, in which a direct drive motor is movable relative to a workpiece and in which the rotor shaft of the motor carries a saw blade, Underwriters Laboratory requires that the strain relief provided for the motor power cord be capable of transmitting a 35-pound load from the power cord to the structure of the motor without damage to either the power cord or to the lead wire connections within the motor. Heretofore, without the provision of adjustable clamp strain reliefs, it has been difficult to ensure that the power cord would be reliably strain relieved in such manner as to transmit such high loads to the motor, especially when variation in thickness of the power cord within a reasonable tolerance is taken into account. However, adjustable clamp strain relief systems typically included a screw-type clamp which required separate installation and assembly operations and which could work loose during operation of the motor.